What makes Mars a long-term case study in planetary atmospheric stripping?

It lost its magnetosphere and subsequently most of its atmosphere

Mars is considered a vital long-term case study because its planetary history illustrates the direct consequences of losing a protective magnetic field. The magnetosphere normally shields a planet's atmosphere from being gradually stripped away by solar wind and charged particles emanating from the Sun. When Mars lost this crucial shield, its atmosphere, which was once thicker, was subjected to relentless erosion by solar radiation over billions of years. This process led to the vast thinning of the Martian atmosphere we observe today, providing a natural, long-duration experiment showing how planetary atmospheric viability is fundamentally dependent on internal geophysical processes like maintaining a magnetosphere. Earth is currently protected from this mechanism, but monitoring Mars helps contextualize the long-term risks to our own atmospheric stability.